The invention generally relates to demulsifying processes, and more particularly demulsifying processes involving water-in-oil emulsions.
Extensive efforts have been made towards breaking, i.e., destabilizing, water-in-oil emulsions, particularly water-in-crude oil emulsions. Crude oil is often found in a reservoir in association with gas and saline formation water. As a reservoir becomes depleted, a time is typically reached when water is coproduced with oil. The number of wells now producing water with crude oil present therein is steadily increasing. Typically these immiscible fluids are readily emulsified by the simultaneous action of shear and pressure drop at the well head, chokes, and valves.
It has long been recognized that the resulting water-in-oil emulsions can be remarkably stable. Moreover, it is understood that asphaltenes are the predominant stabilizer of water-in-oil emulsions produced during the production, transportation, and refining of crude oil. Currently, the primary means by which these emulsions are destabilized is through the addition of polymeric demulsifying chemicals, usually based on phenol formaldehyde resin chemistry, as well as other water-soluble polymers. See e.g., U.S. Pat. No. 5,100,582 to Bhattacharyya; U.S. Pat. Nos. 5,460,750 and 5,525,201 to Diaz-Arauzo, and U.S. Pat. No. 2,446,040 to Blair, Jr.; xe2x80x9cThe Efficiency of Polyalkylenepolyamines formaldehyde ethoxylates as Demulsifiers for Water-in-Crude Oil Emulsionsxe2x80x9d, N. N. Zaki, Tensides Surfactants Detergents 34(1), pp. 12-17 (1997) and xe2x80x9cPolyoxyethylenated Bisphenol-A for Breaking Water-in-Oil Emulsionsxe2x80x9d, Zaki, N. N., Polymers for Advanced Technologies, 7, pp. 805-808 (1996). These resins, particularly, comb polymers, often possess alkylated phenol hydrophobic moieties and ethoxylated hydrophilic moieties. These materials may be disadvantageous in that they pose potential environmental risks since they are believed to be endocrine disrupters. Moreover, such materials are often very costly.
Other means of destabilizing asphaltene-stabilized water-in-oil emulsions include thermal pressurization and rapid depressurization (see e.g., U.S. Pat. No. 5,948,242 to Ohsol), along with electrostatic droplet shattering and coalescence (see e.g., U.S. Pat. Nos. 5,607,574 to Hart and U.S. Pat. No. 5,746,908 to Mitchell). These methods tend to focus on efforts at xe2x80x9ccrackingxe2x80x9d or xe2x80x9cdisruptingxe2x80x9d the rigid, viscoelastic film of asphaltenes which form around the water droplets. One disadvantage of these techniques relates to the reforming of water droplets due to re-adsorption of displaced or xe2x80x9cdisruptedxe2x80x9d asphaltenic film fragments in shear fields.
There is a need in the art for methods of destabilizing water-in-oil emulsions which address the problems discussed above.
In one aspect, the invention provides a method of demulsifying a water-in-oil emulsion. The water-in-oil emulsion comprises an oil phase and an aqueous phase. The oil phase comprises asphaltenes. The method comprises contacting a carbon dioxide containing fluid with the emulsion such that the carbon dioxide containing fluid enters the oil phase of the emulsion. Advantageously, the asphaltenes precipitate out of the emulsion and the emulsion destabilizes.
In another aspect, the invention provides a composition of matter. The composition of matter comprises a water-in-oil emulsion comprising an oil phase and an aqueous phase, as well as a carbon dioxide containing fluid. The oil phase comprises asphaltenes. The carbon dioxide containing fluid enters the oil phase of the emulsion, such that the asphaltenes precipitate out of the emulsion and the emulsion destabilizes.
These and other aspects and advantages of the invention are set forth in detail herein.
The present invention now will be described more fully hereinafter with reference to the accompanying specification and examples, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
In one aspect, the invention relates to a method of demulsifying a water-in-oil emulsion comprising an oil phase and an aqueous phase. The oil phase comprises asphaltenes. The method comprises contacting a carbon dioxide containing fluid with the emulsion such that the carbon dioxide containing fluid enters the oil phase of the emulsion, wherein the asphaltene precipitates out of the emulsion and the emulsion destabilizes. Although not intending to be bound by theory, it is believed that when the asphaltenes precipitate, they begin to flocculate and agglomerate from the oil phase. Additionally, it is believed that the carbon dioxide containing fluid diffuses into the oil phase of the emulsion to render the asphaltenes interfacially inactive, i.e., the state of the phase of the asphaltenes changes, such that the emulsion destabilizes.
For the purposes of the invention, the term xe2x80x9cwater-in-oilxe2x80x9d emulsion has a meaning that is conventionally known in the art, and refers to an emulsion in which the oil phase is the continuous phase and the aqueous phase is the dispersed phase. In a preferred embodiment, the emulsion comprises at least about 20 percent by volume of the oil phase, and more preferably from about 20 to about 90 percent by volume of the oil phase. In another embodiment, the oil phase comprises from about 1 to about 10 volume percent of the aqueous phase, i.e., about 90 to 99 percent of the oil phase.
The oil phase which is present contains a number of hydrocarbon materials that are typically present in water-in-oil emulsions, the selection of which is known to those skilled in the art. In a preferred embodiment, the oil phase includes mineral oils, particularly in the form of petroleum oil or petroleum-derived oil (e.g., Petroleum Refinery Products). Petroleum oil preferably encompasses aliphatic or wax-base oil, aromatic or asphalt-base oil, or mixed base oil. Crude oil, particularly heavy or light oil is particularly preferred. The term xe2x80x9cheavy oilxe2x80x9d refers to crude oil having an API gravity less than 20 and a viscosity higher than 100 cp and up to 10,000 cp at 20xc2x0 C. In a typical embodiment, heavy crude oil has a relatively high asphaltene content with a relatively low H/C ratio. The term xe2x80x9clight oilxe2x80x9d refers to crude oil having an API gravity higher than 20 and a viscosity less than 100 cp at 20xc2x0 C. In a typical embodiment, light crude oil has a relatively low asphaltene content with a relatively high H/C ratio. See e.g., The Chemistry and Technology of Petroleum, 2nd Ed., James G. Speight, (1991), pp. 3-5. Preferred crude oils that are employed in the method of the invention includes, but is not limited to, Arab Berri, Hondo, and B6 crude oils.
For the purposes of the invention, the term xe2x80x9casphaltenesxe2x80x9d is defined to be components of the high boiling point fraction of the crude oil which are composed of polynuclear aromatic hydrocarbons of molecular weights ranging from 500 to 2000 or greater and aggregate molecular weights of up to 20,000 joined by alkyl chains. See e.g., Hawley""s Condensed Chemical Dictionary, 12th Ed., Richard J. Lewis, Sr., Editor, (1993), p. 101. Various amounts of asphaltenes may be present in the emulsion. For example, in a preferred embodiment, the emulsion may include from about 0.2 or 15 to about 25 or 30 percent (w/w) of asphaltenes. In another embodiment, the emulsion may include from about 25 to about 30 percent (w/w) of asphaltenes. In another embodiment, the emulsion may include greater than about 25 percent (w/w) of asphaltenes. It should be appreciated that other amounts are encompassed by the invention.
The aqueous phase includes water. For the purposes of the invention, the term xe2x80x9cwaterxe2x80x9d is to be broadly construed and may include, but not be limited to, deionized water, tap water, distilled water, or ground water, or combinations thereof. Preferably, the water is present in a crude oil system. The aqueous phase may include any number of different additives (e.g., scale inhibitors, corrosion inhibitors, H2S scavengers, and biocides), buffers, and the like, the selection being known to one skilled in the art.
In one embodiment, the aqueous phase may include at least one inorganic salt. Examples of inorganic salts include, without limitation, sodium chloride, calcium chloride, magnesium chloride, sodium carbonate, and magnesium sulfate. Mixtures thereof can also be used. The aqueous phase may contain various amounts inorganic salts. In a preferred embodiment, for example, the aqueous phase comprises from above about 0 to about 10 weight/volume percent.
For the purposes of the invention, carbon dioxide may be employed in the carbon dioxide-containing fluid in a liquid or supercritical phase. If liquid CO2 is used, the temperature employed during the process is preferably below 31.04xc2x0 C. If supercritical CO2 is used, it is preferred that the phase be employed at high pressure above 1070 psi and temperature above 31.04xc2x0 C. As used herein, the term xe2x80x9chigh pressurexe2x80x9d generally refers to CO2 having a pressure from about 1000 to about 4500 psi. In a preferred embodiment, the CO2 is utilized in a xe2x80x9csupercriticalxe2x80x9d phase. As used herein, xe2x80x9csupercriticalxe2x80x9d means that a fluid medium is above its critical temperature and pressure, i.e., above 31.04xc2x0 C. and above 1070 psi for CO2. The thermodynamic properties of CO2 are reported in Hyatt, J. Org. Chem. 49: 5097-5101 (1984); therein, it is stated that the critical temperature of CO2 is 31.04xc2x0 C.; thus the method of the present invention may be carried out at a temperature above 31.04xc2x0 C. A preferred pressure of the carbon dioxide containing fluid ranges from about 1000 or about 3000 psi to about 4500 psi. A preferred temperature of the carbon dioxide fluid ranges from about 25xc2x0 C. to about 70xc2x0 C., more preferably from 50xc2x0 C. to about 70xc2x0 C., and most preferably from about 60xc2x0 C. to about 70xc2x0 C. In general, embodiments in which the temperature is 50xc2x0 C. or higher are particularly preferred.
The method of the invention may take place over various time periods, the selection of which may be determined by a person who is skilled in the art. Preferably, the step of contacting the carbon dioxide containing fluid with the emulsion is carried out from about 5 minutes to about 24 hours, and more preferably from about 5 minutes to about 2 hours.
The carbon dioxide containing fluid may include other components such as, for example, co-solvents, surfactants, co-surfactants, buffers, rheology modifiers, biological agents, and viscosity reduction modifiers. Other components may be used in the carbon dioxide containing fluid, the selection of which may be determined by the skilled artisan.
A wide variety of co-solvents can be used. Exemplary co-solvents include, but are not limited to, n-pentane, hexanes, cyclohexane, n-heptane, methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, methyl-isopropyl ketone, benzene, toluene, xylenes, terpenes, paraffins, and mixtures thereof.
The co-solvents may be used in various amounts. In a preferred embodiment, the carbon dioxide containing fluid preferably comprises from about 0.1 weight/volume percent to about 5 weight/volume percent of co-solvent based on the volume of the emulsion.
If desired, a surfactant can be used in the carbon dioxide containing fluid. These surfactants are known to those skilled in the art. Examples of suitable surfactants are set forth in U.S. Pat. Nos. 5,783,082; 5,589,105; 5,639,836; and 5,451,633 to DeSimone et al., the disclosures of which are incorporated herein by reference in their entirety. Preferably, the surfactant has a xe2x80x9cCO2-philic segmentxe2x80x9d, i.e., a segment that has affinity for carbon dioxide. The xe2x80x9cCO2-philic segmentxe2x80x9d preferably contains a fluorine-containing segment, typically in the form of a fluoropolymer. In various preferred embodiments, the surfactants can also include a xe2x80x9cCO2-phobicxe2x80x9d segment which is preferably covalently bonded to the CO2-philic segment.
Exemplary CO2-philic segments may include a fluorine-containing segment or a siloxane-containing segment. The fluorine-containing segment is typically a xe2x80x9cfluoropolymerxe2x80x9d. As used herein, a xe2x80x9cfluoropolymerxe2x80x9d has its conventional meaning in the art and should also be understood to include low molecular weight oligomers, i.e., those which have a degree of polymerization greater than or equal to two. See generally Banks et al., Organofluorine Compounds: Principals and Applications (1994); see also Fluorine-Containing Polymers, 7 Encyclopedia of Polymer Science and Engineering 256 (H. Mark et al. Eds. 2d Ed. 1985). Exemplary fluoropolymers are formed from monomers which may include fluoroacrylate monomers such as 2-(N-ethylperfluorooctanesulfonamido) ethyl acrylate (xe2x80x9cEtFOSEAxe2x80x9d), 2-(N-ethylperfluorooctanesulfonamido) ethyl methacrylate (xe2x80x9cEtFOSEMAxe2x80x9d), 2-(N-methylperfluorooctanesulfonamido) ethyl acrylate (xe2x80x9cMeFOSEAxe2x80x9d), 2-(N-methylperfluorooctanesulfonamido) ethyl methacrylate (xe2x80x9cMeFOSEMAxe2x80x9d), 1,1xe2x80x2- dihydroperfluorooctyl acrylate (xe2x80x9cFOAxe2x80x9d), 1,1xe2x80x2-dihydroperfluorooctyl methacrylate (xe2x80x9cFOMAxe2x80x9d), 1,1xe2x80x2,2,2xe2x80x2-tetrahydro-perfluoroalkylacrylate (xe2x80x9cTANxe2x80x9d), 1,1xe2x80x2,2,2xe2x80x2-tetrahydro perfluoroalkylmethacryland other fluoromethacrylates (xe2x80x9cTMxe2x80x9d); fluorostyrene monomers such as xcex1-fluorostyrene and 2,4,6-trifluoromethylstyrene; fluoroalkylene oxide monomers such as hexafluoropropylene oxide and perfluorocyclohexane oxide; fluoroolefins such as tetrafluoroethylene, vinylidine fluoride, and chlorotrifluoroethylene; and fluorinated alkyl vinyl ether monomers such as perfluoro(propyl vinyl ether) and perfluoro(methyl vinyl ether). Copolymers using the above monomers may also be employed. Exemplary siloxane-containing segments include alkyl, fluoroalkyl, and chloroalkyl siloxanes. More specifically, dimethyl siloxanes and polydimethylsiloxane materials are useful. Mixtures of any of the above may be used.
Exemplary CO2-phobic segments may comprise common lipophilic, oleophilic, and aromatic polymers, as well as oligomers formed from monomers such as ethylene, xcex1-olefins, styrenics, acrylates, methacrylates, ethylene and propylene oxides, isobutylene, vinyl alcohols, acrylic acid, methacrylic acid, and vinyl pyrrolidone. The CO2-phobic segment may also comprise molecular units containing various functional groups such as amides; esters; sulfones; sulfonamides; imides; thiols; alcohols; dienes; diols; acids such as carboxylic, sulfonic, and phosphoric; salts of various acids; ethers; ketones; cyanos; amines; quaternary ammonium salts; and thiozoles.
In another aspect, the invention relates to a composition of matter. The composition of matter comprises an oil phase and an aqueous phase of a demulsified water-in-oil emulsion; and a carbon dioxide containing fluid. The carbon dioxide containing fluid entered the oil phase of a water-in-oil emulsion such that asphaltenes precipitate out of the oil phase of the emulsion and the emulsion destabilizes. The composition of matter preferably has an asphaltene content of no greater than 15 percent by weight, although may contain other asphaltene amounts as set forth in detail hereinabove. The features described in the composition of matter are set forth in greater detail hereinabove.